The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Internal combustion engines, especially automotive internal combustion engines, generally fall into one of two categories, spark ignition engines and compression ignition engines. Known spark ignition engines, such as gasoline engines, function by introducing a fuel/air mixture into the combustion cylinders, which is then compressed in the compression stroke and ignited by a spark plug. Known compression ignition engines, such as diesel engines, function by introducing or injecting pressurized fuel into a combustion cylinder near top dead center (TDC) of the compression stroke, which ignites upon injection. Combustion in both known gasoline and diesel engines involves premixed or diffusion flames that are controlled by fluid mechanics.
Known gasoline engine systems are throttled at light-load and part-load operating conditions to limit the inducted trapped air mass into the engine as a means of controlling the engine load. This throttled engine operation results in high pumping work that limits the fuel economy potential of the gasoline engine.
Known variable-valve actuation (VVA) systems may reduce pumping losses by operating the engine in regimes that reduce the effective displacement of the engine. Known operating systems include Early-Intake Valve-Closing (EIVC) and Late-Intake-Valve-Closing (LIVC) VVA strategies. Known LIVC systems can have limited benefits when using a discrete two position switching mechanism and lack of continuous cam phasing.
Cam phasing is known whereby intake camshafts, exhaust camshafts or both intake and exhaust camshafts are continuously adjustable within limits to effect controlled phasing of all of the respective intake and exhaust valves actuated by the respective camshaft.
Fully flexible variable valve actuation is known whereby timing, duration and lift of individual valves are controlled via various implementations including electronically, hydraulically and combinations thereof.
One known diesel engine includes a single overhead camshaft carrying intake cams for intake valve actuations and exhaust cams for exhaust valve actuations. The camshaft includes concentric inner and outer shafts. One of the intake and exhaust cams are rotationally fixed to the inner shaft and the other of the intake and exhaust cams are rotationally fixed to the outer shaft. Relative phasing of the intake and exhaust cams can thereby be adjusted whereby relative phase control of the intake and exhaust valves serviced by a single camshaft can be adjusted. However, all intake valves are commonly phased and all exhaust valves are commonly phased.